The present invention relates to a method of making globular or spherical bodies of optical quality and an apparatus for performing this method.
Principally this sort of method is known from JP-H11-199250 A. In this method preferably cylindrical glass gobs are placed in receptacles in a heat-resistant support and are heated. Globular bodies form from the cylindrical glass gobs under the action of surface tension. The glass gobs are retained in the receptacles under vibration in this phase. The globular bodies so formed serve as optical lenses, for example in telecommunication equipment or also in CD players.
During heating of the glass gobs undesirable influences can occur at the contact positions between the glass gobs and the heat-resistant support during precise temperature guidance. The glass can stick or, more seriously, attach to the walls of the receptacles when the glass gobs have a certain viscosity. The resulting globular bodies with corresponding surface faults or defects are no longer universally usable. At best they can be aligned during usage so that these defects or faults are not aligned in the path of rays traveling through the optical system. However this is only possible with great effort and corresponding expense. The consequences of attachment of glass to the material of the support are still more serious. They must be replaced, whereby considerable additional costs result.
JP-08-277133 discloses an additional method for making globular bodies. In this method a melted glass gob is placed in a receptacle with a trumpet-shaped opening, while gas is conducted from a small hole into the receptacle from below so that the melted glass gob does not come into contact with the interior surface of the receptacle. The glass gob is gently rotated and accordingly forms the globular body. First of all, the passage, through which the gas is conducted, must have a diameter of at least 300 μm because smaller passages are built into the support only with much effort or expense. In this known method temperature inhomogeneities result at the surface of the melted glass gob. Thus the surface region of the glass gob, which is directly exposed to the gas flow, is somewhat cooler than the opposite part of the spherical surface. This leads to internal stresses in the globular body and to additional shape variations and in sum total to optical aberrations. The internal stresses in the globular body could generally be avoided by expensive tempering of the gas flow.